New Machine Build- All steel design and build, complete walkthrough

[hawkmoon77]

Preface

After assembling an enourmous amount of data on the project, I thought it best to funnel it all to one place, and I can think of no better place than CNCzone. My intention of this thread is to completely follow the process of a home-built CNC machine from start to finish (and by start, I mean the start of design, not the start of assembly).

• Machine Summary: All steel construction, with precision linear motion parts. Precision carving of wood, and light metal work. Cost range of 4K to 6K.

• Machine Design Criteria: X travel of 5 to 6 feet, Y travel of 3 to 4 feet, Z travel 9 to 12 inches. 600 to 900 pounds or less. Accuracy of .003 inches or better. Modest speeds, but speed is second to accuracy. Relative ease and repeatability of assembly with minimial avanced tools.

• Scope of Thread: While my goal is to have all information about my machine in one organized place, there are limitations. I will not be walking through the basics of CNC parts and construction. There are so many wonderful and helpful guides on that subject, that I would just be re-inventing the wheel. I will consider all such material to be introductory. I will also not focus on any software, modeling, CAD or CAM theory. Such will be considered outside the bounds of this thread. This guide will begin with machine design and end with completed construction and testing.

I thank you all in advance for taking an interest in this thread, and hope to be able to give back a bit to CNCzone. I'd also like to thank Haydn and Madvac for the unmeasurable amount of guidance and information they unknowingly contributed to my project.

*** The information I post throughout this thread is for archival purposes only, and only intended as a historical account of the decisions I made, and the actions I took. I AM NOT QUALIFIED TO GIVE ANY ADVICE ON THESE TOPICS. All information is provided without guarantee or warranty. You assume all risks. Please be safe and smart in your endevours.

[hawkmoon77]

Table of Contents

Section I: Design

Chapter 1 - Introduction, POST #5

Chapter 2 - Xaxis Support Design, POST #6, POST #7, POST #15

Chapter 3 - Bed Design, POST #16, POST #17

Chapter 4, Table Bracing, POST #24

]
Section II: Table Build

Section III: Gantry Build

Section IV: Electrical

Section V: Final Details

Sectino VI: Testing

[hawkmoon77]

RESERVED 1

[hawkmoon77]

RESERVED 2

[hawkmoon77]

SECTION I: Design

Chapter 1, Introduction

Design is, at the very least, as important as the build. I do not want to waste money or time building a machine that does not function as I intend. It is with that premise that I begin this very critical phase.

My overall design objectives include a balance of precision and budget, with liberties taken to reduce weight, size and cost where possible. I also plan on using readily available parts, and will not rely on any dumpster finds. My goal includes a certain potential for repeatability in construction and cost.

Throughout this section, I'll refer often to the weight differences between alternative configurations. Building a lighter machine isn't just about transportability. Most metal suppliers determine their pricing by the pound, and not by the shape. The final weight of the strutural components of the machine, multiplied by the price/pound figure, will give me a reliable cost estimate. Bottom line is that saving weight is saving money.

Another consideration is the general availability of the tools required to construct the project. While I will require more than a hammer and drill, my plans have included special consideration for minimizing the types of advanced tooling that is not generally available. I know noone in a machine shop, and I don't own a metal lathe, mill or welder. Nonetheless, the ultimate design of the machine takes into account this disadvantage. Other than leveraging the machine itself to aid in its own construction, few advanced tools should be required.

I rely very much on CAD software for both modeling and (more importantly) simulation and testing of loads, forces, and other design stresses. I will not bolt any parts together because it seems like the right thing to do. Rather, my design will be thoroughly and methodically tested and simulated to achieve the objectives I laid out. If for example, I need the deflection of a part to stay within .001 in. at a given load of 300 pounds, then I will rely on my simulation software and actual mechanical testing to demonstrate that capability. Over-engineering (in the way of extra braces or thicker materials) only adds cost and weight, and so my design seeks to meet its design objectives using the minimum amount of readily available parts.

Within the next few chapters, I'll share my design choices, as well as the results of some load tests and simulations. Further refinement is required, but only few design choices remain.

[hawkmoon77]

Chapter 2: Xaxis Support Design

I will be walking through my design method for the development of each component. Rather then just simply show or describe my decisions, I will present the methodology used to make them as well. Below describes my progression through the Xaxis design.

Picture #1 shows a basic side profile of the longitudinal side of the table that will support the Xaxis linear slide (visible in the first and second picture). The two corner legs are extended above the rail and will support the bed. Although there will be some interaction between the bed and the Xaxis rail, I am treating them seperately at this stage of the design.

Notice that there exists a longitudinal brace connecting the two outside legs. This is rather standard protocol, as it will prevent the legs from kicking out when weight is applied. Analysis of the benefits of the bottom brace showed that it added negligable benefit to any actual load bearing capabilities of the Xaxis rail (the beam at the top that will hold the Xaxis linear slide).

A major concern is overall stability when the gantry moves across the Xaxis. Even with bottom brace, there exists a danger that the machine will shutter and shake with quick changes in gantry direction. Acknowledging that the machine will have to be installed on a floor surface made truly level, I am making the decision (for various benefits) to anchor the machine directly to the floor. In my case, it will be bolted into a cement floor. Because of the floor's rigidity, the bottom brace becomes completely unnecessary, saving approximately 23 feet of structural steel tube and 126 pounds, while making gains in overall stability. See Picture #2, which introduces a steel plate at the bottom of each leg that will be bolted to the floor.

Initial load analysis is presented in Picture #3. Discplacement is over-exaggerated for better visualization; actual discplacement measurements are provided in the chart. At the center of the Xaxis rail is a load of 300 pounds applied over 1 square inch. I am assuming a gantry weight of 300 pounds, spread across two rails (150 each), with a safety factor of 2... thus my decision to model 300 pounds. Displacement is predicted to be .426mm at its worst (the center of the Xaxis rail). Note that the longitudinal beam that supports the top of the bed will add additional stability. The tops of the corner legs currently bend toward one another, but an additional bed beam will add compression strength to stabilize the legs, resulting in less Xaxis rail displacement. Modeling of that beam isn't necesary at this point.

I will need to keep maximum displacement at nearly .1mm to stay within the tolerances of the linear rail and my overall design criteria. Clearly I will need additional support along the Xaxis rail, but I want to avoid unnecessary steel. I may need multiple braces, a third center leg, or both. I will present my findings in the next update.

[hawkmoon77]

Chapter 2: Xaxis Support Design, cont.

In this section, I'll walkthrough three bracing configurations that do well to summarize the dozens of configurations I modeled. I've added the bed longitudinal beam (the gray beam visible in Picture #1) as it's presence is relevant for these tests. Note also the addition of the corner leg braces. Load testing is the same as that described in the previous portion of this chapter; the scale is normalized for all trials.

Picture #2: Brace centered to leg, narrow angle to Xaxis Rail
Combined Weight = 8 pounds per side
Combined Length = 28 in. per side
Displacement = .266 mm.

Picture #3: Brace near bottom of leg, narrow angle to Xaxis Rail
Combined Weight = 17.5 pounds per side
Combined Length = 53 in. per side
Displacement = .192 mm.

Picture #4: Brace near bottom of leg, wide angle to Xaxis Rail
Combined Weight = 22 pounds per side
Combined Length = 65 in. per side
Displacement = .182 mm.

The results do not fare well for the the side braces. All three trials showed displacement greater than .1 mm.

Also worth noting is the diminishing returns of added material with regards to the reduction in displacement. As the braces elongated, weight and length jumped up, while displacement remained materially similar. Additionally, when the brace length is maximized so that each brace extends from the floor of the corner leg to the center of the Xaxis rail (I did not include a picture of this configuration), weight is increased to 30 pounds per side, length reaches 86 in. per side, and displacement along the Xaxis rail is in some places reduced by .002 mm., while increased in other places by as much as .04 mm. This arrangement is hardly beneficial.

It is clear that at these lengths, the Xaxis rail will need a third leg.

[garagon127]

Hawkmoon77,
Thank you for taking the time to share this endeavor with this community. I will be watching with great enthusiasm and wish you the best of luck! Sounds like you know what you're doing.

Gary

[garagon127]

Hawkmoon77,
Knowing that it is early in the design stage, I thought you might like this video of a pinion roller drive system that I thought would be great for a CNC machine. Here is a link to a video from Nexen group ( I have no affiliation to them) that I stumbled on one day.

‪Roller Pinion System‬‏ - YouTube

‪Roller Pinion System‬‏ - YouTube

This is so smooth and precise...someday I hope will be in MY future!

Gary

[hawkmoon77]

Thanks for the info Garagon,

I've seen those systems before, but haven't seen a video that demonstrated it so clearly. I understand that those systems are pretty good. When used with a servo, they are very fast and precise.

[asuratman]

Hello,
Goodday, anybody here use this nexen RPS system? Do you know about the cost approximately for specific size? I think its expensive.

[Eddymeister]

Thats interesting reading there hawkmoon...

I can understand your thinking as I'm in the initial phase of designing... Building a machine to a set of specs is definitely more cost effective in the long run rather than selecting a component bolting it together and hoping for the best...

What program are you using to give you such results... Is that Solidworks by chance...

I'm no engineer but have the patience and passion to learn about this...
My preliminary design is based around large PFC or Post formed channels to create the gantry and X Axis substrate...
Would you know of any simple programs that would help me test my design as you have...?

I'm an aussie but 300 pounds of gantry sounds incredibly heavy...? Isnt that around 120Kgs? Or is this a figure that include max cutting loads as well with a built in margin for error...

Good post mate...
Keep it up..